First of all, a general synchronization channel (SCH) will be described.
In a multiple carrier mobile communication system, for example, an orthogonal frequency division multiple (OFDM) communication system, a user equipment (UE) receives a synchronization channel (SCH) to initially access a base station. In this case, the user equipment can acquire timing synchronization and frequency synchronization of a signal transmitted from the base station. Afterwards, the user equipment sets up communication with the base station by acquiring cell information and/or system information through a broadcasting channel (BCH) and a reference symbol, if necessary, as well as the aforementioned synchronization channel.
Meanwhile, the aforementioned synchronization channel (SCH) can be classified into a primary synchronization channel P_SCH and a secondary synchronization channel S_SCH depending on its function. For example, since a code sequence of the primary synchronization channel P_SCH is used equally in every cell, the user equipment can perform timing detection and frequency correction of a signal transmitted from a specific cell even in case that the user equipment does not know a cell to which the user equipment belongs. A code sequence of the secondary synchronization channel S_SCH depends on information (for example, cell ID, CP length, etc.) of a cell to allow the user equipment to obtain information of either a cell to which the user equipment is connected or a neighboring cell after acquiring timing.
FIG. 1 is a flow chart illustrating a method for performing initial cell search by using a synchronization channel (SCH).
First of all, in steps S101 and S102, the user equipment starts and acquires initial OFDM symbol timing and frequency synchronization by using the SCH. Then, in step S103, the user equipment acquires frame synchronization by using the acquired timing and frequency synchronization. At the same time, in step S104, the user equipment acquires cell related information such as cell ID, and completes an initial procedure for access to the base station in step S105.
As described above, the synchronization channel (SCH) which is important for initial cell search of the user equipment should be received regardless of a system band of a cell which the user equipment wishes to access even in case that several system bands exist within one system (i.e., in case where a scalable bandwidth is supported). For example, in a 3GPP LTE system which is currently being discussed, several system bandwidths of 10 Mhz, 5 Mhz and 1.25 Mhz can exist within one system.
FIG. 2 illustrates a bandwidth where the SCH is located in a scalable bandwidth.
Specifically, FIG. 2 illustrates a method for positioning the SCH in a frequency band in case where three transmission bandwidths of 10 Mhz, 5 Mhz and 1.25 Mhz exist within one system as described above. As shown in FIG. 2, the current 3GPP LTE system is based on that the SCH is allocated to the smallest bandwidth of 1.25 Mhz among bandwidths of 10 Mhz, 5 Mhz and 1.25 Mhz which the system can support, so that the user equipment can receive the SCH no matter what the user equipment uses any bandwidth.
To effectively transmit the SCH which is important for initial cell search of the user equipment, it is preferable that a transmitting side allocates more transmission power to the SCH than that of other channels, thereby increasing detection probability of a receiving side. However, if a limited power resource is first allocated to a specific channel, it may affect allocation of transmission power resources of other channels.